Sorry, extra3d, ich is still in your tank. You may be temporally "managing'' it or getting a short reprieve, but its there. You have done nothing to kill it. Ich often is "invisible", but its still there. Either in a non-feeding stage, in the gills, or other hard-to-spot location on fish.
Keeping stress low can delay the inevitable, but not prevent it. Nothing you are doing kills ich. Good water, good feeding, vitamins, etc., are part of just good husbandry that everyone should practice. The ich can (and will) reappear at any time. There are countless "stressors'' that could trigger an ich onslaught that are not within your control; a power outage (dropping temps), a fish death (ammonia), a fish reaching sexual maturity and becoming aggressive, just to name a few. Even without a major stressor, ich is going to be come a big problem for you; its just a matter of the timing.
I know a few people have seen ich return after treating it; but (IMO & IME) it is almost always because of some small error in the treatment process. Attention to detail when treating parasites is vital. Just a few minutes lapse in SG, Cu level, or whatever, is all the time an newly released ich theront needs to find a fish host and keep the cycle going. I also think it is possible, but very unlikely, that the parasite could have an offspring that was very resistant to the treatment. Simply the huge numbers of ich parasites present and the ability of tiny creatures to ''morph'' make this a distant possibility. Don't hang your hat on this, but I'm just covering all the bases. I have never encountered it and know nobody who can document it. But, I was told by a parasitologist (there really is such a job) at a major University SW aquaculture lab, that it was possible.
I sure don't have a degree in this stuff, just lots of experience. Prior to moving, I was ''recruited" by 3 LFS on a fairly regular basis, to help customers with parasites. The number of fish I've kept, and prophylactically treated for ich , numbers in the hundreds and I've never seen an ich infestation (or individual parasite0 that couldn't be killed. I now have over 1000 gallons of fish (not counting sump) and I have no ich. I have seen many tanks like yours: ich was there , then gone. But it always came back. Unfortunately, in the time I've spent on this forum, I've heard of countless accounts like yours. I have never heard anyone say "my tank has now been ich-free for a year!" If I did hear this, I would suspect that ich wasn't the proper diagnosis in the first place. I'm sure not trying to crush your excitement; just trying to state my opinion and experience.
I hope you will properly treat ich and hope other folks don't get a false sense of security from your "cure"; thus delaying real treatment. I know this is a windy response to a point that is very typical on our forum and there are several great posts above on the subject. I hope someone will benefit from all the info on this thread.